The use of a polyol in the preparation of polyurethanes by reaction of the polyol with a polyisocyanate in the presence of a catalyst and perhaps other ingredients is well known. Conventional polyols for flexible polyurethane foams, such as slab urethane foams, are usually made by the reaction of a polyhydric alcohol with an alkylene oxide, usually ethylene oxide and/or propylene oxide, to a molecular weight of about 2,000 to 5,000 and above. These polyols are then reacted with polyisocyanate in the presence of water or other blowing agents such as fluorocarbons to obtain polyurethane foams. Polyols have been modified in many ways in attempts to improve the properties of the resulting polyurethane, for example, by using a polymer polyol as the polyol component. Conventional polyols may be used as the dispersing media or base polyol in these polymer polyols.
For example, dispersions of polymers of vinyl compounds such as styrene, acrylonitrile or a mixture of the two (abbreviated as SAN monomers), or a polyurea polymers such as those prepared from toluene diisocyanate (TDI) and hydrazine in conventional polyols have been included to improve the properties of the polyols, and thus, the properties of the resulting foam. Polyurethane foams with higher load bearing properties (ILD - indentation load deflection or CFD-compression load deflection) may be produced in this manner. It would be desirable if polymer polyols could be prepared which would be stable andhave low viscosities. Stability is important to the storage life of the polyols before they are used to make the polyurethane foams. Low viscosities and small particle sizes are important in a good quality polyol to permit it to be pumped easily in high volume foam producing equipment.
It would further be desirable if styrene/acrylonitrile polymer polyols could be synthesized which would have large SAN ratios. The substitution of styrene for acrylonitrile in these polymer polyols helps prevent discoloration during the cure of the polyurethane, and also helps improve flame retardability of the resultant foams. However, the stability of the polymer polyols decreases with increasing styrene to acrylonitrile ratios. That is, the components tend to separate out upon standing during storage. The viscosity and particle size of the resultant polymer polyols are also adversely affected.
U.S. Pat. No. 4,119,586 to Shah contends that the use of a minor amount of a higher molecular weight (HMW) polyol in conjunction with a major amount of a lower molecular weight polyol results in stable, lower viscosity dispersions and permits comparatively higher polymer contents. The lower limit or minimum amount of HMW polyol found to be necessary is around 5%, preferably 10%, of the total polyol. As the HMW polyols are generally more expensive to make and use in comparison to the lower molecular weight polyols, it is desirable to reduce their proportions in the polymer polyols as much as possible. Relatively large amounts of the HMW polyols may also have adverse effects on foam physical properties, and may reduce the hydroxyl number of the final polymer polyol.
Further, the inventors in U.S. Pat. Nos. 3,953,393 and 4,458,038 contend that high styrene content polymer polyols can be prepared by conducting the in situ polymerization in the presence of an alkyl mercaptan as a chain transfer agent in specially formulated, unsaturated polyols where specified and ostensibly critical amounts of unsaturation are necessary. However, the use of alkyl mercaptans in polyurethanes is undesirable because of malodorous qualities of the foams made with these materials. The pungent nature of these chemicals and the foams therefrom render them unacceptable to the consumer, and often to the manufacturer.